Personally I don't think his hind end is that disproportionate to the rest of him, it is slightly undermuscled but that is from lack of work, not some underlying conformational issue or a lack of overall balance in body structure. JMO.
Pros: Seems like he has a nice soft mouth and they aren't worrying him with bits or training aids which is good as you can get all the basics right from the start. He has a nice athletic body, good shoulder and an alert and intelligent eye.
Cons: I know they say he has started dressage training but he seems to be laterally quite stiff and also heavy on the forehand. But that is just a training issue and easily fixed. Hard to tell from the pics but his pasterns look a bit steep, different photos would clarify that. Big huge problem for me is the breathing, that would be enough for me to pass him over, particularly as an eventing prospect as you need maximal oxygen exchange, even in the lower levels.
All horses deserve, at least once in their lives, to be loved by a little girl.